1. Field of the Invention
The present invention relates to a laminate film for electrophotography for easy production of an information recording medium using an image-recorded medium printed by an electrophotographic method, an information recording medium using the laminate film, and a manufacturing method of the information recording medium. More specifically, the present invention relates to a laminate film for electrophotography, an information recording medium using the same, and a method for manufacturing the information recording medium, which laminate film can be used for non-contact or contact type information recording media containing personal image information such as facial-photograph-containing cash cards, employee identification cards, student identification cards, individual membership cards, resident identification cards, various types of driver's licenses and various types of qualification certificates, RFID tags, image-recorded sheets for personal identification used in medical settings, image display boards, indication labels, and the like.
2. Description of the Related Art
In recent years, image formation technology has developed, and means are known which can form images of the same quality in large quantities at low cost by various printing methods, such as intaglio printing, letterpress printing, planographic printing, gravure printing, and screen printing. Such printing methods are also widely used for manufacturing an information recording medium which can store predetermined information and communicate with an external device in a contact or non-contact manner, such as an IC card, a magnetic card, an optical card, and a card which is a combination thereof.
However, for example, the above-mentioned screen printing requires a lot of printing plates corresponding to the number of images to be printed. In the case of color printing, the required printing plates are further increased corresponding to the number of colors. Therefore, these printing methods are not suitable for individual pieces of personal identification information (including facial photographs, names, addresses, dates of birth, various licenses, and the like).
In response to the above-mentioned problem, the most dominant image formation means currently used is an image formation method based on a printer or the like which employs a sublimation-type or melting-type heat-transfer method using an ink ribbon, or the like. However, while such means can easily print personal identification information, they still have a problem in that increase in the printing speed lowers the resolution, and increase in the resolution leads to decrease in the printing speed.
In image formation (printing) by the electrophotographic method, the surface of an image carrier is electrically charged uniformly, and then subjected to light exposure according to image signals, to form an electrostatic latent image based on the difference in potential between the exposed portion and the unexposed portion. Thereafter, electrostatic development is conducted with a color powder (an image forming material) called toner with the opposite polarity to (or with the same polarity as) that of the charge of the image carrier, thereby forming a visible image (a toner image) on the surface of the image carrier. In the case of a color image, the color image is created by repetition of this process plural times or by processes conducted by plural image formation units disposed in parallel to form a color visible image wherein the color visible image is transferred to an image recording medium and fixed (immobilization, in other words, melting of the color powder mainly by heat followed by solidification thereof by cooling).
Since an electrophotographic method electrically forms an electrostatic latent image on the surface of an image carrier by an image signal as mentioned above, not only can the method form the same image repeatedly but also can easily form a different image. Moreover, a toner image formed on the surface of an image carrier can be substantially completely transferred to the surface of an image recording medium, and the toner image slightly remaining on the surface of the image carrier can be easily removed by a resin blade, a brush or the like. Accordingly, printed materials can be easily prepared for limited production of a wide variety of goods.
In addition, the above-mentioned toner is generally formed by fusing and mixing a thermally fusible resin and a pigment, as well as optional additives such as a charge control agent, and then pulverizing and atomizing the kneaded substance. Further, the electrostatic latent image in the electrophotographic method has a considerably higher resolution compared with the above-mentioned atomized toner, and a sufficient resolution on par with the resolutions realized by the screen printing and the heat-transfer method using an ink ribbon can be expected.
Also, a color image can be obtained by using color toners of four primary colors of cyan, magenta, yellow, and black and then mixing the toner images of the respective colors. Theoretically, the same colors as realized in printing can be reproduced. In addition, in the above-mentioned color toner, the toner resin and the pigment can be relatively freely compounded, thereby enabling easy increase in the light shielding property of the image.
There have been almost no studies on the heat resistance and light resistance of information recording media intended to be used outdoors. Particularly when a driver's license or the like is left in a car and exposed to direct sunlight, fading occurs if the image is a heat-transferred image using a dye as a coloring material. However, when a color image is formed by the electrophotographic method, pigments corresponding to the respective colors of cyan, magenta, yellow, and black used in the color toner have excellent light resistance. Therefore, the light resistance of the images formed by the electrophotographic method is considered to be sufficiently high. Likewise, if a heat-resistant toner is selected, the heat resistance of the image formed on an information recording medium is considered to be high enough to allow the information recording medium to be used outdoors.
On the other hand, the most widely used substrates (cores) used for various types of cards are currently polyvinyl chloride sheets. This is because polyvinyl chloride (hereinafter sometimes referred to as “PVC”) sheets are excellent in printing characteristics in conventional printing machines, because they are also excellent in suitability for embossing (process to raise or lower characters and the like), and particularly because they are inexpensive compared with other alternate resins.
Although in recent years people have an environmentally negative image of PVC due to the release of dioxins by incineration treatment, it is thought today that the harmful gas release can be suppressed by proper incineration methods and the advancement of incinerators. The PVC resins to be raw materials comprise salts at a ratio of about 60%, and from the standpoint that the petroleum content thereof is low as compared with other resins, they are sometimes thought to be less harmful to the environment than other resins. Further, PVC resins are excellent in recyclability, and material recycling in the field of credit cards is advanced.
If embossing is not carried out in the manufacturing of cards, conventional films such as biaxially stretched PET (polyethylene terephthalate) films can be used. However, in order to retain the functions of conventional cards, embossing is often indispensable. Films currently used for embossing include: ABS resin films and polyolefin resin films, which soften at relatively low temperatures; a modified PET resin film called PETG; and integrally formed films of a modified PET resin film with a PET film, an amorphous PET resin film, or a polycarbonate resin film.
As a method for producing conventional cards using substrates of the above-mentioned various types of cards, a production method including carrying out multi-imposition printing of card designs on large size substrates, layering the substrates so as to adjust the card thickness, sandwiching them with metal plates, piling more than ten of the layered products, heat pressing them at one time under atmospheric pressure followed by cooling, and punching the pressed products into a card size is generally employed.
This method takes several tens of minutes for the heat pressing so as to evenly transmit heat to the center part of the layered products and expel the air remaining between substrates, and takes approximately the same time for cooling.
On the other hand, examples of the above-mentioned various kinds of cards printed by using an electrophotographic apparatus are as follows.
To improve the fixation property and durability of images and prevent forgery and falsification, there is a method proposed (refer to Japanese Patent Application Laid-Open (JP-A) No. 10-86562) which involves forming a hot sealing type adhesive layer of a polyester type on a transparent sheet containing polyethylene naphthalate or polyethylene terephthalate; printing image information for authentication and identification thereon as a mirror image; and sticking an acrylic substrate and the mirror image face to face in a contacting manner (the transparent sheet also works as a protection sheet).
However, with respect to the above-mentioned transparent sheet bearing the adhesive layer, although the fixation property and the transportability are taken into consideration for use in electrophotography, since the sheet is just an insulating sheet for which no particular consideration of the transfer property is taken, there are cases where this results in inferior image quality in an electrophotographic apparatus. Further, since no practical description of the speed and pressure of laminating means is given, even if an image is printed on the transparent sheet, air may possibly remain between the sheets, and the adverse effects of air bubbles sometimes result in inferior image quality.
As another example, to form good images and to prevent forgery, a method has been proposed (refer to JP-A No. 11-334265) which involves printing individual identification information on a light transmitting sheet as a mirror image; and sticking an adhesive layer on a substrate having an IC memory and the mirror image face to face in a contacting manner (the light transmitting sheet also works as a protection sheet).
However, with respect to the light transmitting laminate sheet (and the substrate), there is description that it is preferable to use a biaxial orientation polyester film or ABS or a polyester film/biaxial orientation polyester film for at least a portion of the sheet, and that it may be polyvinyl chloride, and since just a insulating sheet is used without any particular special device, transportation failure may possibly occur in an electrophotographic apparatus and the image quality may possibly become inferior. Also, since there is no practical description of the speed and pressure of laminating means, even if images can be printed on the light transmitting sheet, air may possibly remain between sheets at the time of laminating them, and the effect of the air bubbles remains to result in deterioration of the image quality.
Further, as another example, there is a method proposed (refer to JP-A No. 2001-92255) which involves printing an invisible bar code as well as various kinds of individual information on a 250 μm-thick polyvinyl chloride sheet or a 280 μm-thick polyester sheet by an electrophotographic method; overlaying a 250 μm-thick polyvinyl chloride over film or a 100 μm-thick polyester vinyl over film on the printed surface; and laminating by a heat press.
However, with respect to the above-mentioned polyvinyl chloride sheet or polyester sheet, since just an insulating sheet is used without any particular special device, transportation failure may possibly occur in an electrophotographic apparatus, and the image quality may possibly become inferior. Further, since there is no practical description of the temperature, pressure and time of the heat press apparatus, even if images can be printed on the sheet, air may possibly remain between the above-mentioned sheets and the over films and between the over films and a press member of the heat press apparatus at the time of laminating them, and the effect of the air bubbles remains to result in deterioration of the image quality and glossiness.
Further, as another example, to suppress glare of a non-laminate surface of a substrate, a laminate film for electrophotography has been proposed (refer to JP-A No. 2004-12575) which has a gloss control layer provided on the non-laminate surface, wherein the gloss control layer contains a binder (polyester resins or the like) and a filler (fine particles=mat agents) and has a thickness in a range of 0.01 to 20 μm (more preferably 0.1 to 5 μm), a volume average particle diameter of the filler is in a range of 0.1 to 10 μm (more preferably 1 to 5 μm), and the weight ratio of the filler and the binder (filler:binder) is in a range of (0.3:1) to (3:1), as well as an image recording medium having a gloss control layer almost same as that of the laminate film for electrophotography and an image display body using the medium (refer to JP-A No. 2004-20950).
With respect to the above-mentioned laminate films for electrophotography, the non-laminate layers are previously subjected to mat treatment to control the surface gloss of the non-laminate surfaces after the laminate films for electrophotography and core substrates are laminated. However, at the time of laminating the laminate films for electrophotography and the core substrates, air may possibly remain between the laminate films for electrophotography and a press member of a heat press apparatus, and the effect of the air bubbles remains to result in deterioration of the gloss quality.
As described above, in the case of using conventional laminate films for electrophotography, air remains between the layered members to result in deterioration of the gloss and image quality.
However, these problems may be often solved if the layered products obtained by layering the substrates constituting the cards as described above are heat pressed slowly taking sufficient time of about several tens of minutes at the time of heat pressing. On the other hand, the heat pressing taking such a long time considerably lowers productivity. Therefore, in terms of productivity, the heat pressing is preferably completed within as short a time as possible.
Accordingly, it is thought that it is easy to improve the productivity in the case where a layered product has a thin thickness since heat can promptly be transmitted to the center part of the layered product. However, since the time taken to sufficiently expel air remaining between substrates is independent of the thickness of the layered product and thus not practically changed, the productivity cannot be improved even if heat pressing is carried out while the thickness of the layered product is made thin.
Further, if the heat press time is forcibly shortened, lamination is completed before the air remaining between substrates is sufficiently removed to leave air bubbles between the substrates. Dent traces (dimple patterns like the surface of a golf ball) of air remaining appear on the outermost surface of the substrate contacting a metal plate utilized for heat pressing to result, in particular, in considerable deterioration of the finished gloss quality of cards.